The present invention relates to process methods of treating food waste sludge, and more particularly to a process method of converting the DAF (dissolved air floatation) skimming sludge of a food processing plant into a value added product with good nutritional value for feed and fertilizer nutritional applications and precipitating molasses sludge from a sugar processing plant into a product with much more hardness and less moisture absorption.
The waste water from a food processing plant has high BOD (biochemical oxygen demand), FOG (fats, oils and grease), SS (suspended solids) and TKN (total Kjeldahl nitrogen). Dissolved air floatation (DAF) units are used in meat, milk product, snack food processing and waste water treatment plants. The primary purpose is to reduce BOD, SS, FOG and TKN in the waste water passing to sewage. But it creates another problem to dispose of the pasty and oily skimming sludge, which is separated into the top portion because of the low density. The waste skimming sludge has very attractive nutrientsxe2x80x94protein, fat, carbohydrate and minerals.
Animal meat industry is a major industry to use dissolved air floatation (DAF) units to reduce BOD, SS, FOG and TKN in the waste water passing to sewage. Animals are grown and slaughtered to meet people""s needs every year, which includes beefs, pigs, chickens, turkeys and others. In the animal processing industry, an average of 4.5 kg of protein is lost to the sewer for every 454 kg of live weight kill (Ockerman and Hansen, 2000). The percentage is about 1%. If half of the protein now lost to the sewer were recovered, there would be at least an additional 181 million kg of protein each year, worth perhaps $ 400 million from animal processing in the United States (Hansen, 1983). It is very important to use animal wastes and by products for economic and public health achievements.
The skimming sludge from a meat processing plants has about 12% solid with about 40-45% fat and 45-40% protein in solid basis. The solid level can be increased by a dewatering equipment. But it is not easy process. U.S. Pat. No. 4,767,537 discloses a dewatering process for increasing the solid content of sludge with a digester and nitrate ions.
There are four methods to deal with the skimming sludge. The common method is for land application, which causes a pollution problem. The fee for a mid-size animal processing plant with 13 truck loads of the skimming sludge per week is about $150,000 per year for the land application. Also the potential nutritive value of the skimming sludge is lost through microbiological degradation. Another method is to use microorganisms for anaerobic or aerobic lagoon treatment to break down the organic matters. The additional cost and equipment are involved in the treatments. Land application and lagoon systems on large-scale farms can pollute water sources and should not be used. But there are no other feasible and affordable methods. The third method is to heat the skimming sludge and to centrifuge it into fat, solution and solid layers. But the separation is not good. There also are mixtures between fat and solution layers and between solid and solution layers. Then the three major products are processed and used separately. The additional equipment is involved. The fourth method is to blend the skimming sludge with other by products. But the blended product price is decreased significantly. For example turkey meal price is about $300 per ton without turkey DAF skimming sludge or $225 per ton with turkey DAF skimming sludge. The difference is $75 per ton. Also the dry process cost is high because the skimming sludge has about 88% moisture. All four methods are not economic methods. These methods have been discussed in the book xe2x80x9cAnimal By-Product Processing and Utilizationxe2x80x9d (Ockerman and Hansen, 2000). U.S. Pat. No. 6,235,339 discloses a process method to treat a meat processing waste stream with different chemicals. U.S. Pat. No. 5,514,388 discloses a process to treat a protein with a base to increase the pH to a strong basic endpoint at first. Then fat is added into the alkali protein. The protein gel is formed when the pH is lowed to an acidic endpoint with an acid. U.S. Pat. No. 5,595,717 discloses a process to cause additional quantities of silica to precipitate out of the geothermal water as particles. These particles have high surface area for improving energy recovery. This U.S. patent relates to silica precipitation, which does not relate to food DAF skimming sludge. If the DAF skimming sludge can be converted into a nice precipitate at low process cost, the nutrients can be recovered and converted into good nutritional products easily. Also the dry process cost can be reduced because the extra water can be removed and the precipitate particles have high surface area. There is a need for an inexpensive process, which can convert food DAF skimming sludge into a value added product.
It has been found DAF skimming sludge with low density, which floats on the top portion, can be precipitated and separated from the solution after precipitating with animal blood under a heat treatment. The precipitate can bind most nutrients together. Some food or feed grade chemicals such as phosphate acid, phosphate salt, calcium, ethylenediamineteraacetic acid, ethylenediamineteraacetic salt, polyphosphate, sorbic acid, sorbate salt, bisulfite salt and antioxidants can be used to help the process and product. After forming the binding precipitate, the density of the product with the skimming sludge is increased significantly. So the product can sink and precipitate from the top portion to the bottom portion with high recovery yield for these nutrients after a centrifuge process. For example 95% of the protein can be recovered. The separation is very good. The extra water can be removed by a centrifugation, screen, decant or press process to increase the solid level and to reduce the dry process cost. The process and product can limit the problems of waste pollution and high dry process cost. The two raw materials of DAF skimming sludge and animal blood can be easily mixed in an animal slaughter plant and processed by a heat treatment. The product has low bacterial accounts. The products may have by pass function for ruminant animals for more milk production. The skimming sludge, which is often for land application with a fee, can become value added nutritional ingredients for feed and other nutritional applications. The value of the final dry product from the typical mid-size animal processing plant is more than $1,200,000 per year.
The purpose of the present invention is to provide a practical precipitation process for binding most nutrients together, converting the food waste sludge into value added products, recovering more materials, reducing dry process cost, increasing product value and reducing waste pollution problem.
Molasses is a sugar liquid waste by product from a sugar processing plant. Lactose is another sugar liquid waste by product from a cheese or whey protein processing plant. These carbohydrate sugars are often concentrated into a viscous sludge at solid from 40-75% for delivering to customers. The sugars become very viscous when the moisture becomes less and less. The viscosity can be reduced with a heat treatment. The sugar by products are used as liquid sludge for feed applications because the dry process is an expensive process. Molasses is often used to make block products as self feed supplement applications for beefs and cows, which are described by U.S. Pat. Nos. 6,168,803, D440,362, 5,755,178, 5,622,739, D375,181, 4,731,249 and 3,961,081. Dehydrated nutrients such as proteins, minerals and vitamins are mixed with the molasses after molasses is heated and vacuumed to low moisture level such as 5%. But the block products become soft easily because it can absorb moisture from air easily. Various attempts have been made to improve the properties of animal block feed products such as hardness, moisture absorption, foam and storage life over the years. U.S. Pat. No. 6,168,803 discloses to use at least alkaline earth metal oxide to improve the block feed product. U.S. Pat. No. 6,143,333 discloses to use magnesium oxide for fish attractant block. U.S. Pat. No. 4,731,249 discloses to use the polymer of polyvinyl alcohol for solidifying the block feed product. The process of the present invention is to use animal blood proteins to improve the block properties such as less form, more hardness, less moisture absorption and longer storage life. This process may have more nutritional benefits and lower process cost over other methods. It has been found that animal blood at low percentage rate such as 3-10% in solid basis can increase the block hardness and reduce moisture absorption significantly. The new block feed products may have longer shelf life because of more hardness and less moisture absorption. This process may help feed companies to produce better molasses block feed products for providing the products to dairy and beef farmers. Besides the block products, it also has been found that this precipitation process with high animal blood percentage rate such as more than 15% in solid basis can precipitate the sugar by products into solid particles to reduce the dry process cost significantly, which could save the industry millions of dollars. The dry products can be used for different applications easily.
The present invention provides a simple and practical process to form a precipitate for converting DAF (dissolved air floatation) skimming sludge into a value-added product and reducing dry process cost and improving molasses products with more hardness and less moisture absorption.
The final DAF skimming product has good nutritional value and low bacterial counts, which can be used as a good and safe ingredient for nutritional applications. The process could save millions dollars for food industry every year.
DAF skimming sludge can be mixed with animal blood easily. Direct or indirect heat is applied to form a precipitate for binding most nutrients together when the temperature is above 70xc2x0 C.
The pH value of the mixtures can be adjusted for stronger precipitation. A centrifugation, screen of press process is applied to remove the extra water. A general dry process may be used to dry the product. Some food or feed grade chemicals can be used for the process and product. If a wet product is used for making a product with other ingredients, a dry process is not necessary.
Dry process cost can be reduced because the water in the precipitate can be removed by a centrifugation, screen, decant or press process and the precipitate has more surface area comparing to the raw materials. The final product has low bacterial counts such as E. coli, salmonella, total coliforms, yeast, mold and staphylococcus. Also this process limit the waste pollution problem from land application and lagoon treatments.
The present invention also provides the same simple and practical process to form a precipitate for improving molasses block products with more hardness, less moisture absorption and longer shelf life. Also the sugar by products can be dried into solid particles at low dry process cost by this precipitation recovery process.
The following examples set forth preferred methods in accordance with the invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.